The present invention relates to an impact fastening tool including a torque detection means, and a torque tester.
An impact fastening tool is designed to automatically stop its driving part, when a tightening torque for a screw such as a bolt and a nut reaches a set value.
The tightening torque as the set value is detected by attaching a sensor to a rotating portion (e.g., attaching a strain gauge to a main shaft), and transmitting a signal from the rotating portion to the non-rotary housing side. An example of the means for transmitting the signal is a contact point that is allowed to rotate by adopting a slip ring portion, as disclosed in Japanese Patent Laid-Open No. 2014-79817.
However, since the impact fastening tool generates intermittent impacts, the impact fastening tool using the slip ring portion has a problem that the intermittent impacts momentarily separate (bounce) a fixed connector using a brush, wire, or other parts from a rotating electrode. Since this interrupts signal transmission, a torque detection means misses a signal. Then, as shown in FIG. 8, if a force F is increased to press a brush B, which is the fixed connector, against the rotating electrode to prevent the aforementioned bouncing, the brush B and rotating electrode 4 abrade quickly and service life is reduced. This is because only one end of the brush B is fixed, as shown in FIGS. 8 and 9.
Another impact fastening tool, as disclosed in Japanese Patent Laid-Open No. 61-4676, includes multiple coils to form rotary transformers, so that nothing comes into contact with a rotating portion. However, the impact fastening tool including the rotary transformers requires multiple coils, and is therefore large, heavy, has many parts, and has a problem that the impact may break the coil.